This invention relates generally to pressure sensors for in vitro measurements and more particularly to a catheter tip pressure transducer of small size for insertion within the body, for example, in the blood vessels.
As medical science has advanced, various accurate measuring devices have been developed and are used in diagnosing techniques. Particularly, in the diagnosis and research of the circulatory system, a method for measuring intravascular and intracardiac pressure precisely is needed in order to determine the pressure distribution within blood vessels or within the heart. For this purpose, it is preferable to measure pressure without inserting the measuring device into the living body. However, it is impossible to achieve this objective in view of the technical level of the present medical science. Presently local blood pressures must be measured by inserting the measuring device into the living body and blood vessels directly. One such measuring device is a catheter manometer. The catheter manometer is inserted into the body portion where a measurement is required; pressure at that portion is transmitted through a fluid filling the inside of the catheter, for example, a saline solution, which serves as a pressure transmitting medium. The catheter is connected to a pressure transducer which is located outside the living body. In this way, the pressure is detected electrically.
However, in such a device, large errors may occur under the influence of the compliance of the catheter and the diaphragm of the pressure transducer, and the movement and viscosity of the fluid within the catheter. As a result, significant distortion can occur in the pressure waveform produced by this transducer. Furthermore, if air bubbles are intermixed with the fluid within the catheter, the distortion of the pressure waveform becomes more pronounced such that the data obtained from the catheter becomes significantly lacking in reliability.
In order to overcome the drawbacks in the manometer transducer, efforts have been made toward the disposition of a pressure transducer utilizing a semiconductor, which will be located at the tip portion of the catheter. In such an arrangement, the pressure transducer is used in vitro to obtain measurements. Unfortunately, the data obtained from such transducers of the prior art is distorted as a result of thermal stresses which exist within the transducer primarily related to differential expansion of dissimilar materials.
What is needed is a catheter tip pressure transducer which can accurately measure pressure in vitro without being influenced by the thermal stress which occurs in the supporting members of the transducer.